The present invention relates to high-Tc superconducting ceramic oxide products, and macroscopic and microscopic methods for making such high-Tc superconducting products. The high-Tc superconducting ceramic oxide products of the present invention have a high critical current density, high critical magnetic field, long life, and are capable of being recharged or having superconductivity regenerated.
Since the initial discovery of high-Tc superconductivity in metal-oxide ceramics, many people have tried to determine the underlying physical origin of this superconductivity. It is generally agreed that the microstructure of the CuO2 plane of high-Tc superconductors plays a key role in high-Tc superconductivity. Viewed in two dimensions, there are four oxygen atoms around a single Cu atom in high-Tc metal-oxide superconducting ceramics (in three dimensions, there would be six oxygen atoms around one Cu atom), and each Cu atom can supply at most three electrons to its nearest neighbors. This means that there can be no stable valence bond between the Cu atoms and the oxygen atoms. The Cu electrons are, therefore, only weakly localized and can pass across the oxygen bridges to complete quantum tunneling. Such collective quantum tunneling plays the key role in the high-Tc superconductivity. Since the exchange interaction between the two Cu ions is mediated via the oxygen ions, the extra spin of a hole localized on the oxygen will have a big effect. Designating the two Cu ion spins by S1 and S2, and the O by, the would prefer to be parallel or antiparallel in respect to both S1 and S2. The spins of high-Tc superconductors are, therefore, very disordered. The local spin wave function is either symmetric or antisymmetric and is rapidly changing with time, because of the mixed valence resonance vibration. The disordered spin wave function will be automatically adjusted to accompany the tunneling electrons.
The present invention relates to new methods of making completely sealed high-Tc superconducting products using metallic oxide ceramics, and to the completely sealed high-Tc superconducting products produced thereby. The inventive methods and products are based on the realization that the oxygen content of the metal-oxides plays an important role in high-Tc superconductors and products incorporating the same. Below a critical oxygen content Xc1(O), or above a critical oxygen content Xc2(O), superconductivity is destroyed. The transition temperature Tc changes in between these critical concentrations. For example, for the superconducting oxide system YBa2Cu3Ox, Xc1(O)=6.5 and Xc2(O)=7.0. Experiments show that if oxygen atoms escape from high-Tc superconductors, thereby lowering the oxygen content to less than the critical oxygen content Xc1, the superconductivity of the metal-oxide is destroyed. If the oxygen content is then increased, for example by sintering the oxygen-depleted metal-oxide ceramic within a predetermined temperature range in the presence of oxygen, the superconductivity will be restored. The principal point is that for YBa2Cu3Ox superconductors, the oxygen content X(O) must satisfy the equation 6.5 less than (O) less than 7.0, and for all high-Tc oxide superconductors the oxygen content X(O) must satisfy the equation Xc1 less than X(O) less than Xc2.
The high-Tc superconductivity state of oxide ceramics is only a metastable state, and the superconductive oxide ceramics will tend to lose oxygen to become a stable state insulator. This process of oxygen loss may take a few hours, a few days, a few months, or even a few years or longer depending upon the conditions surrounding the superconductive oxide including temperature, atmosphere, and the like. However, regardless of how long the oxygen loss process may take, the tendency of the metastable superconductive state to change to the stable insulative state is certain. Therefore, to protect the high-Tc superconductivity of oxide ceramics, the oxygen content of the ceramic corresponding to the superconductive state must be maintained.
The present invention provides a completely sealed superconducting product whereby the oxygen loss is prevented and a long-lived high-Tc superconducting ceramic oxide product is attained. As described in detail, hereinafter, the seal can be made using metal, plastic or any materials which are inert to oxygen.
The present invention is also based on the recognition that the high-Tc superconductors are ceramic materials, a basic property of which is brittleness. Because of this brittle characteristic of ceramic superconductors, many attempts were made to produce high-Tc superconducting ceramic products using traditional methods to make wires, cables, tapes and the like, and then making superconducting products from the superconducting ceramic-containing wires, cables and tapes. Examples of such wire, cable and tape methods of producing superconducting ceramic products include: U.S. Pat. Nos. 4,952,554; 4,965,249; 4,975,416; and 4,973,574. Other methods of making superconducting ceramic products are shown, for example, in the following U.S. Patents: U.S. Pat. Nos. 4,975,411; 4,975,412; 4,974,113; 4,970,483; 4,968,662; 4,957,901; 4,975,414; and 4,939,121.
However, all of these prior attempts to make high-Tc superconducting ceramic oxide products suffer from one or more disadvantages. The wire and cable making methods typically include a drawing or working step to reduce the diameter of the superconducting ceramic oxide product. Such drawing and working steps are liable to break the brittle ceramic oxide product, therefore the breaking and sintering cycles will repeat again and again and the resulting wires have poor flexibility and discontinuity caused by breaking. This is called xe2x80x9ccrackxe2x80x9d and xe2x80x9csausagexe2x80x9d problems in HTSC wire making. Further, prior attempts to produce superconducting ceramic products have not had the high mass density necessary to achieve high current density, have had an insufficient ratio of superconducting cross-sectional area to non-superconducting cross-sectional area, and have suffered undesirable oxygen loss resulting in loss of superconductivity. In addition, prior methods of making high-Tc superconducting ceramic oxide products have been costly, involving expensive materials and numerous, time consuming steps, and have produced products of only limited shapes suitable for only limited applications. Also, prior methods could not, or could not easily, make high-Tc superconducting connections, which is necessary, especially for making a high-Tc superconducting magnet. A key technology for making high-Tc superconductive magnets is the making of zero resistance connections.
This invention also attempts to apply an alternative or a selective waveform pulse magnetic field to destroy the magnetic moment order (which does not do good to the high-Tc superconductivity), to accelerate oxygen to occupy the positions of CuO2 planes, and to orient the CuO2 plane to a desired direction by the dynamic process of the alternate field during the heat treatment. This invention using a dynamic field has high efficiency compared with a static magnetic field. This is because dM/dt=xcex3Mxc3x97H(t), M is magnetization and H(t) is alternate field. The dynamics is very important; therefore, alternate field will rapidly rotate magnetic moment randomly, and create the condition to accelerate oxygen to occupy position on CuO2 plane, because AF local magnetic order resists diffusion of oxygen. Therefore, the applied alternate filed is much better than an applied static magnetic field.
The present invention relates to high-Tc superconducting ceramic oxide products and to macroscopic and microscopic methods of making such products. The superconducting ceramic oxide used to produce the superconducting products of the invention can be any superconducting ceramic oxide (including the Al oxide family) and, for example is an REBa2Cu3O9-xcex4ceramic, wherein RE is one or more rare earth elements from the group Y, La, Eu, Lu and Sc, and xcex4 is typically in the range from 1.5 to 2.5. One specific ceramic oxide for use in the products of the present invention is YBa2Cu3Ox, wherein X is between 6.5 and 7.0. Other examples of suitable high-Tc superconducting ceramic oxides include: Bi2Sr2Ca2Cu3OX, HgBaCaCuO system, (Bi,Pb)2Sr2Ca2Cu3OX, Bi2Sr2CaCu2O8+X, La2xe2x88x92XSrXCuO4+Y and Tl2Ba2Canxe2x88x921CunO2n+3.
The high-Tc superconducting ceramic oxide product of the present invention are produced such that oxygen loss is minimized or substantially prevented and the superconducting properties of the ceramic oxide products are maintained for a substantial, even indefinite, period of time. One method for producing a superconducting ceramic oxide product according to the present invention is a macroscopic method of producing completely sealed high-Tc superconducting ceramic oxide products. This macroscopic method comprises the steps of making a superconducting ceramic oxide powder; providing a hollow body of a material which does not react with oxygen; pressing the superconducting ceramic oxide powder into the hollow body at a net pressure of at least from 5xc3x97104 psi to 1xc3x97107 psi, preferably at least 1.2xc3x97105 psi for YBa2Cu3OX (the pressure will depend upon the material and shape; beside making monofilament HTSC wire or tape, the cross-section may be reduced by deformation, such as by swaging, extrusion, drawing, or rolling; thereafter, the smaller cross-sectional wires may be packed into a larger tube, which is then repeatedly deformed, to form a multifilament HTSC wire or tape); heat treatment the body with the superconducting ceramic oxide powder pressed therein in an oxygen atmosphere at temperatures and for time periods of sintering, annealing and cooling which are sufficient for sintering the ceramic oxide powder; optionally applying a waveform or multiple pulses of alternate magnetic field (from 0.0001 Tesla to 300 Tesla) during the sintering and subsequent heat treatment produce to dynamically destroy local magnetic moment and dynamically accelerate oxygen to occupy positions in the CuO2 planes and dynamically to orient the microscopic CuO2 plane to desired direction to carry high critical current and high critical field, the applied field strength varying with the material and the shape of the products; and then sealing the ends of the body and/or any other openings which may have been formed in the body prior to sintering. Local heat treatment can also be used to make connections between high-Tc superconducting products or a product and superconducting lead. If the superconducting ceramic oxide product has a complicated shape, connections between hollow bodies having the superconducting ceramic oxide powder pressed therein are joined and then a second pressing step is performed to ensure that all connections are filled with superconducting powder continuously without any gaps before sintering.
The completely sealed high-Tc superconducting ceramic oxide products produced by the macroscopic method of this invention may be of any desired shape and size and are suitable for use as high-Tc superconducting magnets, high-Tc superconducting motors, high-Tc superconducting generators, high-Tc superconducting transportation lines, high-Tc superconducting electric energy storage devices, or components thereof, and, in general, may be used for any purpose which requires a superconductor.
The microscopic method of producing a high-Tc superconducting ceramic oxide product of the present invention is also based on the isolation (or xe2x80x9csealingxe2x80x9d) of a superconducting ceramic oxide composition to prevent oxygen loss or diffusion and the resultant loss of superconductivity. The inventive microscopic method of making high-Tc superconducting ceramic oxide products comprises the steps of: making a high-Tc superconducting ceramic oxide thin film on a substrate in situ, optionally with an alternate magnetic field being applied during the in situ making process by electron beam deposition, molecular beam deposition, sputtering deposition, laser ablation or any other suitable means, and optionally then sintering the deposited thin film in a magnetic field in an oxygen atmosphere, if necessary; and removing partial oxygen content by a scanning tunneling electron treatment machine (STETM) from a microscopic domain, e.g., 5 xc3x85 to 1000 xc3x85, of the superconducting ceramic oxide thin film to form a microscopic insulation layer between two high-Tc superconducting domains which form a Josephson junction. High-Tc superconducting products made by the microscopic method of the present invention are particularly useful as high-Tc superconducting chips, high-Tc superconducting electric circuits, SQUIDS, the component thereof.
Therefore, it is an object of the present invention to provide high-Tc superconducting ceramic oxide products which do not suffer from the disadvantages of prior superconducting ceramic products.
Another object is to modify a scanning tunneling microscope machine to a STETM, that is, from a microscope to an electron treatment machine for making microscopic patterns as desired by localized electric current and which not only can be used to produce high-Tc superconducting products but also can be used in the semiconductor industry.
Another object of the present invention is to provide high-Tc superconducting ceramic oxide products which are sealed to prevent oxygen loss and loss of superconductivity.
Still another object of the present invention is to provide a macroscopic method for making high-Tc superconducting ceramic oxide products which does not require conventional wire and cable making techniques such as drawing and cold working.
It is still another object of the present invention to provide a macroscopic method for making high-Tc superconducting ceramic oxide products of a variety of shapes, sizes and configurations.
Yet another object of the present invention is to provide a method for making high-Tc superconducting ceramic oxide products whereby the superconducting ceramic oxide compositions are mechanically, electrically and chemically protected.
A further object of the present invention is to provide macroscopic and microscopic methods for producing high-Tc superconducting ceramic oxide products of high quality and having a long life.
Still a further object of the present invention is to provide a microscopic method for producing high-Tc superconducting ceramic oxide products.
Yet a further object of the present invention is to provide an apparatus and method for forming microscopic insulating layers or domains within a superconducting ceramic oxide thin film.
Another object of the present invention is to provide a method for making continuous superconducting connections between high-Tc superconducting products.
Another object of the present invention is to provide a method using alternate magnetic field during the heat treatment procedure for producing superconducting products, in order to destroy local magnetic moment, to accelerate oxygen to occupy CuO2 plane position, and to orient CuO2 plane to desire orientation dynamically.
These and other object of the present invention will be further understood by reference to the following detailed description and drawings, wherein: